1. Field of the Invention
The invention relates to the use of vinyl chloride-ethylene copolymers for imparting water repellency to construction materials, especially for surface-coating materials such as skim coats, monocouche coatings and joint fillers.
2. Description of the Related Art
Polymers based on vinyl ester, vinyl chloride, (meth)acrylate monomers, styrene, butadiene and ethylene are employed in particular in the form of their aqueous dispersions or water-redispersible polymer powders in numerous applications, for example as coating materials or adhesives for any of a very wide variety of substrates. These polymers are stabilized using protective colloids or surface-active compounds of low molecular weight. Polyvinyl alcohols are generally employed as protective colloids. These products find use in particular as binders in hydraulically setting adhesives such as tile adhesives, and in plasters and levelling compounds based on cements or gypsums.
Skim coats or monocouche and joint fillers are each applications which impose very exacting requirements on the water resistance or water repellency of the finished components. By skim coats are meant very thin finish-coat plasters or smoothing-trowel applications with a thickness of generally 1 to 2 mm. Monocouche is a term for single-coat plasters which also serve as decorative plasters at the same time. In order to meet the water repellency requirements of these applications, the formulations must be hydrophobically modified accordingly.
From DE-A 2341085, EP-A 342609, EP-A 717016 and EP-A 1193287 it is known to add fatty acid esters as water repellents to lime- or cement-bound plasters. A common disadvantage in this case is the hydrophobizing nature of these additives. When dry plasters which include such water repellents are stirred into water, the materials are wetted only poorly, and therefore the processing properties are markedly impaired.
Water-redispersible powders based on homopolymers or copolymers of ethylenically unsaturated monomers are used in the building sector as binders, in combination with hydraulically setting binders such as cement. In building adhesives, plasters, mortars and paints, for example, they serve to improve the mechanical strength and the adhesion. From WO-A 95/20627, WO-A 02/31036 and DE-A 10233933 it is known to use hydrophobizing additives such as organosilicon compounds and fatty acid esters as a component of redispersible powders in dry mortars. This circumvents the problem of the poor wettability and processing properties. The hydrophobicizing effect, however, is dependent on the proportion of the water repellent in the redispersible powder, and therefore cannot be varied arbitrarily.
From EP-A 149098 and EP-A 224169 it is known to use vinyl chloride-ethylene copolymers as an additive to hydraulically setting compositions for the purpose of improving their mechanical strength, especially compressive strength, abrasion resistance, flexural strength under tension and adhesive strength under tension.
An object which existed was to provide a polymer composition in the form of its aqueous dispersion or in the form of its water-redispersible powder which is suitable for use in construction materials for which a very high water repellency effect is required. For joint fillers, modified with 1% by weight of polymer, based on dry mass, the water absorption according to EN 12808 after 3 hours should be ≦5 ml. For skim-coat plasters, modified with 1% by weight of polymer, based on dry mass, the water absorption determined by the method of Karsten is to be ≦2 ml after 300 minutes.